Wet spinning apparatus and process



April 9, 1963 R. D. DENYES ETAL WET SPINNING APPARATUS AND PROCESS Filed July 24, 1959 2 Sheets-Sheet. 1

April 1963 R. D. DENYES ETAL 3,084,384

WET SPINNING APPARATUS AND PROCESS Filed July 24, 1959 2 Sheets-Sheet 2 3,084,384 WET SPINNING AllARATUS AND PROQESS Russell D. Denyes, Maplewood, and John W. Soehngen,

Berkeley Heights, N..l., assignors to Celancse Qorporation of America, New York, N.Y., a corporation of Delaware Filed July 24, B59, Ser. No. 829,397 18 til-aims. (til. 183) The present invention relates to wet spinning of filament-forming materials.

In forming artificial filaments by wet spinning, a solution of filament-forming material is continuously extruded through one or more orifices in a member known as a spinning jet or spinnerette into a coagulant or spin bath which precipitates the filament-forming material into one or more filaments, the filaments being removed from the spin bath and thereafter being dried and/or otherwise treated. In one system, for example, a solution of cellulose triacetate in methylene chloride containing up to about 15 or 20% of methanol is extruded through many orifices into a methylene chloride-methanol spin bath containing a large proportion of methanol to form a tow, i.e. a bundle of filaments, which is continuously drawn out of the spin bath. in practicing this process on a commercial scale special problems are encountered when it is attempted to speed up the process without sacrificing the uniformity or excellent physical properties of the product.

It is accordingly an object of the present invention to provide a novel process and apparatus for wet spinning.

It is a further object of the invention to provide a wet spinning system producing a uniform tow of good physical properties.

Another object of the invention is to provide an improved system for the wet spinning of cellulose triacetate.

Other objects and advantages of the invention will become apparent from the following detailed description and claims, wherein all parts and percentages are by weight unless otherwise specified.

In accordance with one aspect of the present invention there is provided a wet spinning apparatus including a tubular column and a perforated tubular member within said column through which freshly formed filaments travel upon leaving a spinnerette. Means for supplying spin bath and for removing spent spin bath are also provided.

While not wishing to be bound thereby, it is believed that the functioning of the perforated tube can be explained as follows: Passage of the filaments through the perforated tube acts as a pump carrying spin bath in the same direction. in the annulus between the spinning column and perforated tube spin bath moves in opposite direction to that of filament travel and then the spin bat-h ews inwardly through the perforations to be carried al ng with the filaments. As a consequence, in contrast with a spinning column of given inner diameter, use of a perforated tube of said inner diameter minimizes the drag between the filaments and immediately adjacent spin btath, i.e. it reduces the tension on the filaments. Since the tension on the filaments in the spinning column must not be permitted to be so high that the filaments are broken and since the tension increases with increased speed of the filaments, in a given system the inclusion of a perforated tube reduces the tension or permits a higher spinning speed at the same tension. In other respects the I filaments produced when using a perforated tube are comparable to and sometimes better than filaments produced in the absence of such a tube. In addition, it has surprisingiy been found that the tension on the filaments when using a perforated tube is almost independent of the spin bath flow rate, whereas when such a tube is not ice used a decrease in the spin bath flow rate increases hydnaulic drag and increases the tension on the filaments.

The perforate-d tube may be formed of varied materials such as woven gauze, expanded metal, sheet material from which circles or other geometrical shapes have been struck out, or the like. The size of each opening may vary Widely but advantageously is less than 0.2 square inch in area to minimize turbulence. Preferably the area of each opening is less than 0.1 square inch. The number and disposition of the openings can also vary widely; satisfactory results have been achieved, for example, using sheet metal struck with 0.06 inch holes to give from about 20 to 65% of perforate area. The chemical composition of the perforated tube obviously should be such that it is inert to the spin bath and the extruded solution.

The internal cross-sectional area of the perforated tube must of course be sufficient to accommodate the filaments which are to pass therethrough but the diameter need not be constant along the length of the tube. The diameter of the spinning column also need not be constant along its length. While it may be much lacger if desired, the cross-sectional area of the spinning column adjacent the perforated tube advantageously ranges between about 200 and 160()% of that of the perforated tube. The size of the annular space about the perforated tube can be infinite but is generally dictated by practical limits. For example, a 4" diameter outer tube would be about the largest one might use. In addition, the size of the annulus should be kept small in order to generate high enough flow currents for adequate mixing of the return streams in theannulus. Too small an area will lead to cavitation.

The length of the spinning column may be varied within wide limits, depending on the nature of the solution being extruded, the spin bath, the spinning speed, etc. When wet spinning cellulose triacetate in methylene chloride into methylene chloride-methanol at speeds up to about 300 yards per minute or more the spinning column may range from about 30 to i inches and preferably about 40 to 60 inches. It may be longer, if desired, but little is gained by lengthening a column more than needed to ensure adequate coagulation. The column may be somewhat shorter, if desired, especially if the spinnerette is positioned in a spin pot several inches below the bottom of the spin column.

The length of the perforated tube may be varied even more widely. It may extend the full length of the spinning column or it may terminate before the end of the spinning column. For example, if the perforated tube ends about 2 to 4 inches short of the end of the column recycling of spin bath will be better. If this distance is increased, the tension on the filaments is increased with increase in the tenacity of the product at the expense of elongation. The perforated tube may even be longer than the spinning column, extending into the spin pot to surround the spinnerette. If desired the perforated tube may extend only over a relatively short length of the spinning column or, if substantially coextensive with the column, various portions may lack perforations to control circulation of the spin bath.v To be most effective in minimizing spinning tension the perforated tube should encircle that portion of the filaments where most of the draw down occurs due to pulling on the filaments by the take-up device and by the fast linearly flowing bath, since that is where the filaments are most sensitive. While the exact location of this portion will vary in dependence upon the precise spinning conditions, when spinning is effected in a large pot followed closely by i a narrow column in which the linear flow rate of the spin bath is relatively high, the portion of high draw down'generally commences within the column less than about 20 inches and most often between about 2 and 12 inches from the spinnerette.

The novel process and apparatus may be employed in any wet spinning process such as the spinning of viscose into aqueous solutions of salts or acids, the spinning of solutions of acrylonitrile copolymers into aqueous salt solutions, or the like. It is especially useful in the wet spinning of solutions of cellulose organic acid esters, for example the wet spinning of an acetone solution of conventional cellulose acetate into water, and especially the wet spinning of organic acid esters of cellulose containing fewer than about 0.29 free hydroxyl group per anhydroglucose unit, e.g. the wet spinning of a solution of cellulose triacetate in a halogenated lower alkane into a halogenated lower alkane plus a lower alkanol. The concentration of cellulose triacetate may range from about to 25%, and the solvent may contain up to about 15 or of a lower alkanol such as methanol in addition to the halogenated lower alkane which is preferably methylene. The proportions of the components of the spin bath may also vary, depending upon the spin bath temperature. As disclosed in US. application Serial No. 638,414, filed February 5, 1957, the disclosure of which is hereby incorporated herein by reference, the advantage of such spin baths is that for each spin bath temperature a composition exists which will give filaments simultaneously having higher tenacities and elongations than filaments spun into spin baths slightly more or slightly less concentrated, i.e. maximum tenacity and elongation can be produced simultaneously. The concentration of methylene chloride, C, in a methylene chloride-methanol spin bath to give the maximum tenacity and elongation under a particular set of conditions is approximately related to the spin bath temperature in degrees centigrade, T, by the equation C=75%Ti5. If it is desired to obtain highertenacities, for example, the same system may be employed but the conditions such as column design may be changed to increase tenacity at the expense of elongation.

The invention will be further described with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic elevation of a spinning apparatus;

FIG. 2. is a vertical section through a portion of the apparatus shown in FIG. 1, with some parts shown in full; 7

FIGS. 3 to 6 are lateral elevations of other embodiments of perforated tubes; and

FIGS. 7 to 18 are schematic views of other embodiments of spinning apparatus. I

Referring now more particularly to the drawings, in FIGS. land 2 there is shown a spin pot comprising a pot 11 and a lid 12. An annular spin bath distributor 13 is positioned near the bottom of pot 11 and is supplied with spin bath by a pipe 14 extending through the base of the pot. Another pipe 15 supplies spinning solution to a spinnerette 16 within the pot 11 a short distance below lid 12. Above distributor 13 the pot 11 is packed with subdivided material 17 surmounted by a retaining Wire screen 18. A bundle of filaments 19 is extruded through the spinnerette 16, passing upwardly and out of the spin pot into a spinning column comprising a cylindrical section 20, a frus-toconical section 21 and a smaller cylindrical section 22. In flowing from the spin pot 11 to the column section 20, the spin bath and filaments pass through an aperture in lid 12 which is concentric with the column but of smaller diameter, constituting a constriction of reduced cross-section. Upon leaving section 22 of the spinning column, entrained spent spin bath is wiped from the bundle of filaments 19 by wiper guides 23, the spin bath falling into head box 24 from which it is drained ofi by pipe 25 to be purified for further use. The filaments next pass over idler rolls 26 and 27, the former being provided with a tensiometer (not shown) to measure the tension on the filaments in the column; The filaments 19 are lapped about a driven feed roll 28 and skewed idle roll 29, roll 28 setting; the spinning speed.

d From rolls 28, 29 the filaments 19 pass on to be dried and collected.

A perforated tube 30 is positioned concentrically within the spinning column from the lid 12 to the top of section 22. The tube 30 forms an annulus with the column in which spin bath flows downwardly to be drawn through the perforations of the tube by the flow within the tube, as shown by the arrows.

FIG. 3 shows a tube 31 wherein the perforations 32, 33, 34 have a variety of shapes other than circular. FIG. 4 shows a tube 35 made up of portions 36 and 37 having different proportions of perforate areas. FIG. 5 shows a perforated tube 38 having perforate sections 39 and '40 separated by an imperforate section 41. FIG. 6 shows a perforated tube 42 having perforate sections 43 and 44 of dilferent diameters separated by imperforate section 45.

FIG. 7 shows a spinning apparatus in which the column comprises a section 46 connected to a section 47 of larger diameter by a frustoconical section 48. A perforated tube 49 extends from the bottom of section 46 and termi: nates slightly below the top of section 47. The transitional section 48 may be longer, shorter or even substantially zero and its distance from the top of the column may also be varied.

In FIG. 8 the spinning column 50 is of constant diameter and surrounds perforated tube 51 which terminates slightly lower than in FIG. 7.

FIG. 9 shows a perforated tube 52 extending through the aperture in lid 53 to surround the portion 54 of the spinnerette through which the solution is extruded.

In FIG. 10 a perforated tube 55 extends from the spinnerette 56 to the aperture in the spin pot lid 57. A trumpet-shaped imperforate reducing section 58 extends a short distance above lid 57 to the beginning of perforated tube 59.

FIG. 11 shows a Venturi'tube 60, i.e. a tube with a constriction, extending from the aperture in lid 61 to a perforated tube 62 which terminates below the spinning column. In FIG. 12 the Venturi tube 63 is spaced from the bottom of the perforated tube 64 and the perforated tube extends as high as the column.

The structure of FIG. 13 is similar to that of FIG. 1 except for the inclusion of a perforated distributor 65 supplied through line 66 with additional spin bath or another coagulant.

In FIG. 14 the spinning column 67 is stepped and surrounds a perforated column 68 of a diameter equal to that of the aperture in lid 69. A second perforated tube 79 extends from the shoulder in the column 68 to the lid 69. Additional spin bath or coagulant is supplied by pipe 71 to the space between column 68 and tube 70.

FIG. 15 shows a spin pot 72 with a downwardly directed spinnerette 73 and a spin bath supply pipe 74. The spinnerette discharges dope centrally of a trumpet 75 which projects beyond the pot and is perforated at 76. A spinning column 77 surrounds the perforated section 76 and is U-shaped, discharging spent bath into receiver 78, a portion of the spent bath being withdrawn at 79 and a portion being recycled through 80 to the spinning column. Other variations of down, U-tuhe or horizontal spinning can be undertaken as shown, for example, in the several figures in connection with up spinning.

FIG. 16 shows a spinning column 81 having a Venturi tube constriction 82 and an enlarged upper section 83. A perforated tube 84 is positioned in the upper section 83 and terminates below the upper section. Additional liquid may be supplied through pipe 85.

FIG. 17 shows a systemcombining some of the features of P168. 1 and 8. The perforated tube 86 is imperforate over its lowermost portion and terminates below the top of the spinning column.

FIG. 18 is similar to-FIG. 8, except that the spinning column 87 has a portion of reduced diameter 88 above a portion 89 which surrounds and terminates above perforated tube 90.

The invention will be further illustrated in the following examples.

Example I Using the apparatus shown in FIGS. 1 and 2, a 22% solution of cellulose triacetate, having an acetyl value of 61.5% calculated as combined acetic acid, in 91/9 methylene chloride/methanol is extruded at the rate of 2.5 gallons per hour through a spinnerette having 1396 holes of 100 micron diameter arranged over a 1.625 inch diameter circular area on a 2 inch diameter face. The spin bath comprises 43/57 methylene chloride/methanol and is supplied at 32 C. at the rate of 2.64 gallons per minute liters per minute). The filaments are withdrawn at 328 feet per minute (100 meters per minute) under a total tension of about 4.19 ounces. Upon drying the filaments average 2.93 denier and are of satisfactory tenacity and elongation. In this run the spinnerette is positioned 2 inches below the lid of the spin pot which is 6 inches in diameter. The aperture in the lid is 0.63 inch in diameter, as is the inside of the perforated sheet metal tube which has a perforate area of 41% made up of 0.062 inch diameter holes on 0.094 inch centers in staggered rows. The lowermost section of the spinning column is inches high and 3 inches in internal diame- .ter. The uppermost section is 18 inches long and 2 inches in internal diameter and the transitional section is 3 inches long.

The filaments appear stationary within the perforated tube whereas in the absence of the tube they appear to be moving about laterally due to turbulence in the spin bath immediately adjacent the filaments. Observation of the spinning column reveals the annular space between the column and perforated tube as being substantially gas-filled and liquid-free for a height of 2 inches down from the top of the column, with a few bubbles below the gas space and with a small film of liquid on the outside of the perforated tube in this 2 inch space. A few drops of dye deposited into this space reveal the flow pattern of the spin bath, viz. the liquid in the annulus moves down in the annulus and through the perforations into the tube at all heights along the tube, some of the spin bath coming oif with the filaments returning to the annulus for recycling but none of the spin bath being recycled to the spin pot.

Example II The process of Example I is repeated except that the spin bath flow rate is cut in half, the spinning speed increased by 10%, the spinning column is lengthened 3 inches and the perforations in the lowermost 2 inches of the perforated column are closed off, as in FIG. 17. The tension on the tow is almost 50% higher and the physical properties of the filaments are very good. For a distance of 2 inches from the top of the column spin bath follows the contour of the filament bundle, leaving a gasfilled liquid-free annulus below which there are a few bubbles. Dye added at the top of the column reveals spin bath fiows downwardly about the perforated tube and .then smoothly into the tube, recycled spin hath not reaching the spin pot.

Example 111 The dope of Example I is extruded in the apparatus of FIG. 18 in an amount sufficient to give filaments of 321 denier at a spinning speed of 492 feet per minute. The spin bath is supplied at the rate of 1.32 gallons per minute. The spinnerette has 1000 100 micron holes arranged over a 1.25 inch diameter circular area on a 1.5 inch diameter face, disposed 2 inches below the perforated tube which is 0.625 inch in diameter, has a 41% perforate area and is 36 inches high. The spinning column has an overall height of 47.5 inches, is 2 inches in internal diameter over its lowermost 39 inches and 0.5 inch in internal diameter over its uppermost 7.75 inches. There is an annular gas space of approximately the cross-section of the annulus between the perforated tube and spinning column, the gas space extending downwardly for about 15 inches starting from the shoulder in the spinning column, liquid flowing down the wall of the spinning column and the outside of the perforated tube where they border on the gas space. Some bubbles are noted below the gas space. The movement of these bubbles in the annulus evidences recycling. If the spin bath flow rate is doubled the vapor space in the annulus is smaller, presumably due to a decreased tendency for cavitation to occur.

Example IV The apparatus for Example III is employed except that the spinning column is 36 inches long, i.e., the same length as the perforamd tube, and has a 2 inch internal diameter over its whole length. With a spinning speed of 410 feet per minute, a spin bath flow rate of 1.32 gallons per minute and a dope flow rate sufficient to produce filaments of 2.86 denier and good physical properties, the level of spin bath in the annulus be tween spinning column and perforated tube is 8 inches below the top of the spinning column with bubbles extending down an additional 4 inches in the annulus. There is a film of liquid on the outside of the tube. Doubling the spin bath flow rate produces a small improvement in physical properties of the filaments. The level of the bath in the annulus is 1-2 inches below the top of the column and practically no bubbles are visible.

Example V Excellent results are achieved spinning the same dope as in Example I through the same spinnerette at the same speed. In this run, however, the spin bath flow rate is 2.11 gallons per minute. The spinning column is 60 inches long and 3 inches in internal diameter. The perforated tube has a 41% perforate area, is -1 inch in inner diameter and extends, as in 'FIG. 11, from 30 inches below the top of the column to 4.75 inches above the spin pot lid. The perforated tube rests on a concentric Venturi shaped section having 1 inch diameter ends, and a 0.5 inch throat running from the 3rd to the 4th inch below the perforated tube.

Substantially similar results are achieved if methanol is introduced into the annulus between the spinning column and perforated tube at a location 30 inches below the top of the spinning column, using a sparger of the type shown in FIG. 13. The methanol may be introduced at the rate of about 6.5 ounces per minute and the composition of the spin bath supplied to the spin pot ad justed so that the overall methanol concentration in the coagulants is 57%.

In each of the foregoing examples the spin bath and dope is supplied by a positive displacement pump to ensure uniform feed rates.

In the foregoing examples the spinnerettes have had their holes arranged over circular areas and the spinning columns and tubes have been circular in cross-section. These elements may be non-circular if desired, however, e.g. elliptical, approximately rectangular, or the like.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention what we desire to secure by Letters Patent is:

1. A wet spinning apparatus comprising a spinnerette for extruding a filamentary material, containing means including a first portion surrounding said spinnerette and a second portion through which said filamentary material passes from said spinnerette, said first and second portions being separated by a constriction, means for supplying a spin bath to said first portion including the space in front of the face of said spinnerette, a perforated tube surrounding said filamentary material on at least a part of its path through said second portion, and means for withdrawing said filamentary material from said second portion along with spin bath, the movement of said filamentary material and spin bath through said perforated tube causing spin bath in the annulus between said second portion and said tube to be drawn into the tube.

2. An apparatus according to claim 1, wherein said second portion and said perforated tube are approximately equal in length.

3. An apparatus according to claim 1, wherein the internal cross-sectional area of said second portion differs along its length. a

4. An apparatus according to claim 1, wherein said perforated tube commences at said constriction such that there is no access between said first portion and the annular space defined by said tube and said second portion at the boundary between said two portions, and said tube terminates before the end of said second portion.

5. An apparatus according to claim 1, wherein the internal cross-sectional area of said second portion adjacent said perforated tube is at least about 200% of the internal cross-sectional area of said perforated tube.

6. An apparatus according to claim 1, wherein the internal cross-sectional'area of said second portion adjacent said perforated tube ranges between about 200 and 1600% of the internal cross-sectional area of said perforated tube.

7. An apparatus according to claim 1, including means for supplying additional liquid to the annulus defined between said second portion and said perforated tube.

8. An apparatus according to claim -I, wherein said perforated tube commences between about 4 and 20 inches from said spinnerette.

9. An apparatus according to claim 1, wherein said spinnerette is upwardly directed.

10. A wet spinning apparatus comprising a spinnerette for extruding a filamentary material, containing means including a spin pot surrounding said spinnerette, a constriction and a column through which said filamentary material successively passes from said spinnerette, means for supplying a spin bath to said containing means including the space in front of the face of said spinnerette,

means for withdrawing spent'spin bath from said containing means, means for drawing said filamentary material from said spinnerette through and out of spin bath in said column, and a perforated tube surrounding said filamentary material ,on at least a part of its path through said column. 3

11. A wet spinning apparatus comprising an upwardly directed spinnerette for extruding a filamentary material, containing means including a spin pot surrounding said spinnerette, a constriction and an upwardly extending column through which said filamentary material successively passes from said spinnerette, means for supplying a spin bath to said containing means adjacent said spinnerette including the space in front of the face of said spinnerette, means for withdrawing spent spin bath from said containing means adjacent the top of said column, means for drawing said filamentarymaterial from said spinnerette through and out of spin bath in said column,

and a perforated tube surrounding said filamentary material on at least a part of its path through said'column.

12. The process which comprises extruding a filamentary material into a spin bath in a first zone supplied with said spin bath, said spin bath flowing with. said filamentary material through a constricted opening into a second zone provided with a perforated tube surrounding said filamentary material on at'least a part of its path through said second zone, withdrawing said filamentary material along with spent spin bath from said second zone, and recycling a portion of said spent spin bath to the annulus between the boundary of said second zone and said perforated tube, whereby liquid in said annulus is drawn into said tube.

13. The process set forth in claim 12, wherein said filamentary material comprises an organic acid ester of cellulose and is extruded as a solvent.

14-. The process set forth in claim 12, wherein said filamentary material comprises an organic acid ester of cellulose having fewer than about 0.29 free hydroxyl group per anhydroglucose unit and is extruded as a solution in a solvent comprising methylene chloride into a spin bath comprising methylene chloride and a lower alkanol.

15. The process which comprises extruding a solution of cellulose triacetate in a solvent comprising methylene chloride into a spin bath comprising a lower alkanol and methylene chloride in a first zone supplied with said spin bath to form filamentary material, drawing said filamentary material together with spin bath through a constricted opening into a column provided with a perforated tube surrounding said filamentary material on at least a part or" its path through said column, and withdrawing spent spin bath from said column.

16. The process set forth in claim 14, wherein said lower alkanol comprises methanol.

17. The process set forth in claim 15, wherein the filamentary material is drawn out of said column without damage at a speed which would damage the fila mentary material in the absence of said perforated tube.

18. The process which comprises extruding a filamentary material in an upward direction into a spin bath fiowing through a column provided with a perforated tube surrounding said filamentary material on at least a part of its path through said column, supplying fresh spin bath to said column from adjacent the point of extruding said filamentary material, withdrawing said filamentary material along with spent spin bath from said column in an upward direction, and recycling a portion of said spent spin bath to the annulus between said column and perforated tube to move in a direction opposite to' that of said filamentary material, whereby liquid in said annulus is drawn into said tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,850,007 Glover et al Mar. 15, 1932 2,046,577 Sellner et al July 7, 1936 2,700,794 Taylor et al. Feb. 1, 1955 2,732,586 Bradshaw et a1 Jan. 31, 1956 2,905,968 Walker et al Sept. 29, 1959 FOREIGN PATENTS 166,476 Australia Jan. 6, 1956 788,315 Great Britain Dec. 23, 1957 792,238 Great Britain Mar. 19, 1958 solution in an organic- 

1. A WET SPINNING APPARATUS COMPRISING A SPINNERETTE FOR EXTRUDING A FILAMENTARY MATERIAL, CONTAINING MEANS INCLUDING A FIRST PORTION SURROUNDING SAID SPINNERETTE AND A SECOND PORTION THROUGH WHICH SAID FILAMENTARY MATERIAL PASSES FROM SAID SPINNERETTE, SAID FIRST AND SECOND PORTIONS BEING SEPARATED BY A CONSTRICTION, MEANS FOR SUPPLYING A SPIN BATH TO SAID FIRST PORTION INCLUDING THE SPACE IN FRONT OF THE FACE OF SAID SPINNERETTE, A PERFORATED TUBE SURROUND- 